The present invention relates generally to control systems and methods for controlling hybrid electric vehicles, more specifically, the present invention relates generally to battery charge management for hybrid electric vehicles.
Automotive vehicles with internal combustion engines are typically provided with both a starter motor and alternator. In recent years, a combined alternator and starter motor has been proposed particularly for use in hybrid electric vehicles. During initial startup of the vehicle, the starter/alternator functions as a starter. While functioning as a starter, the starter/alternator rotates the crankshaft of the engine while the cylinders are fired.
After the engine is started, the starter/alternator is used as a generator to charge the electrical system of the vehicle.
In automotive applications, the engine may be shut down during stops (e.g., red lights). When the accelerator is depressed, the starter/alternator starts the motor and the engine will resume firing. Thus, many startups may occur over the course of a trip.
The starter/alternator can also be operated as a motor if the state-of-charge management strategy deems it desirable to reduce the state-of-charge of the battery (i.e., xe2x80x9cbleed modelxe2x80x9d) to allow for the collection of regenerative energy via braking.
Another mode of the starter/alternator is providing additional torque (i.e., xe2x80x9cboostxe2x80x9d) to the wheels when the torque of the engine is not enough to meet the driver demand.
During braking hybrid electric vehicles seek to recharge the batteries by recapturing the kinetic energy of the vehicle. Batteries for the hybrid electric vehicles by their nature have a limited operating life. If, during operation, an adequate charge is not maintained the battery life may be shortened.
It would therefore be desirable to control the state of charge of the battery to prolong battery life while achieving the required hybrid functionality.
It is therefore one object of the invention to create calibrateable state-of-charge boundary parameters for this state-of-charge management algorithm for the primary purpose of operating the hybrid electric vehicle in the desired hybrid operating mode, which will have the secondary effect of increasing the battery life of a hybrid electric vehicle.
In one aspect of the invention, a method of charging a battery in a hybrid electric vehicle having a starter/alternator and a battery having a state of charge comprises the step of:
When the state of charge is below a first predetermined value, allowing the charging of the battery through operation of the starter/alternator as a generator; and similarly when the state of charge is below a another predetermined value, allowing the battery to be charged via regenerative braking; and when the state-of-charge is below another predetermined value, keeping the engine on because the battery charge may be too low to restart the engine if it is stopped.
When the state of charge is above another predetermined value, allowing the battery to bleed by, operating the starter/alternator as a motor and when the state-of-charge is above another predetermined value allowing the vehicle to xe2x80x9cboostxe2x80x9d the torque at the wheels to meet driver demand that could not be met by the engine alone, by operating the starter/alternator as a motor, consequently reducing the state-of-charge.
In a further aspect of the invention, a system for an automotive vehicle having an internal combustion engine, an energy storage device and a starter/alternator coupled to the engine includes a controller coupled to the starter/alternator and to the energy storage device. The controller monitors a state of charge of the energy storage device. When the state of charge is below predetermined values for the various hybrid modes of charging, regenerative braking or for keeping the engine on if the SOC is very low, the controller allows charging of the battery through operation of the starter/alternator as a generator. When the state of charge is above predetermined values, the controller allows the battery to reduce the state-of-charge for both the xe2x80x9cbleedxe2x80x9d and xe2x80x9cboostxe2x80x9d hybrid modes by operating the starter/alternator as a motor.
One advantage of the invention is the state of charge manager may be set with some hysteresis to avoid rapid changing between the different modes.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.